Rigging mesh with vertex weights: different weights have the same influence
Even with a weight of 0.001, the vertice will be part of the group and the bone will displace it 100%. I think 0.001 must be the lowest value you can enter. But if you create a second bone, parent it, then give a weight of 0.002 to some of the vertices (vs 0.001 for the same vertices in the previous vertex group), the influence of this second bone on these vertices will be twice the influence of the first bone.